Selectable dual mode test access port method and apparatus

ABSTRACT

A process of selecting alternative test circuitry within an integrated circuit enables a test access port. Scan test instruction data is loaded into an instruction register of a test access port TAP, the instruction data including information for selecting the alternative test circuitry. An Update-IR instruction update operation is performed at the end of the loading to output scan test control signals from the instruction register. A lockout signal is changed to an active state to disable the test access port and enable scan test circuits.

This application is a divisional of application Ser. No. 11/695,928,filed Apr. 3, 2007, currently pending;

This application claims priority under 35 USC 119(e)(1) of provisionalapplication Ser. No. 60/212,244, filed Jun. 19, 2000 and provisionalapplication Ser. No. 60/200,418 filed Apr. 28, 2000.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to provisional application Ser. No.60/207,691, filed May 26, 2000, now U.S. Pat. No. 7,058,862, issued Jun.6, 2006, which is hereby incorporated by reference, and application Ser.No. 09/845,879, filed Apr. 30, 2001, now U.S. Pat. No. 7,003,707, issuedFeb. 21, 2006.

FIELD OF THE INVENTION

The present invention relates generally to integrated circuits and, moreparticularly, to test interfaces exist for integrated circuits and/orcores

BACKGROUND OF THE INVENTION

FIG. 1A illustrates the test architecture of a conventional 1149.1 TAP100. The TAP includes a TAP controller 110, instruction register 112,and set of data registers. The set of data registers includes; (1) aninternal scan register 114, (2) an in-circuit emulation (ICE) register116, (3) an in-system programming (ISP) register 118, (4) a boundaryscan register 120, and (5) a bypass register 122. Of the data registers,the boundary scan register and bypass register are defined by the IEEE1149.1 standard. The other shown data registers are not defined by1149.1, but can exist as optional data registers within the dataregister section of the 1149.1 standard architecture. The TAP controllerresponds to a protocol input on the TCK 124 and TMS 126 inputs tocoordinate serial communication through either the instruction registerfrom TDI 101 to TDO 102, or through a selected one of the data registersfrom TDI to TDO. The TRST 128 input is used to initialize the TAP to aknown state. The operation of the TAP is well known

FIG. 1B illustrates an IC or intellectual property core circuit 130incorporating the TAP 100 and its TDI, TDO, TMS, TCK, and TRSTinterface. A core circuit is a complete circuit function that isembedded within an IC, such as a DSP or CPU. FIGS. 1C-1G illustrate theassociation between each of the data registers of FIG. 1A and the targetcircuit they connect to. The data registers are commonly connected attheir serial input to TDI 101. The data registers are separatelyconnected at their respective serial outputs 104-108 to associatedinputs of multiplexer 103, so that they can be individually selected byan instruction to output data on TDO 102, through FF 132, during a dataregister scan.

FIG. 2 illustrates the state diagram of the TAP controller of FIG. 1A.The TAP controller is clocked by the TCK input and transitions throughthe states of FIG. 2 in response to the TMS input. As seen in FIG. 2,the TAP controller state diagram consists of four key state operations,(1) a Reset/RunTest Idle state operation 200 where the TAP controllergoes to either enter a reset state 202, a run test state, or an idlestate 204, (2) a Data or Instruction Scan Select state operation 206 theTAP controller may transition through to select a data register (DR) 208or instruction register (IR) 210 scan operation, or return to the resetstate, (3) a Data Register Scan Protocol state operation 212 where theTAP controller goes when it communicates to a selected data register,and (4) an Instruction Register Scan Protocol state operation 214 wherethe TAP controller goes when it communicates to the instructionregister. The operation of the TAP controller is well known.

FIG. 3A illustrates a conventional internal scan test port interface 300to an internal scan register 301. The scan test port includes a scaninput (SI) 302, scan output (SO) 304, scan enable (SE) 306, captureselect (CS) 308, and clock (CK) 310 inputs. The CK input may be thecircuits functional clock or it may be a dedicated test clock input. TheSE input is used to place the circuit in a scan test mode. Placing thecircuit in a scan test mode may involve conditioning a circuit input forproviding the SI input, conditioning a circuit output for providing theSO output, and conditioning a circuit input for the CS input, asindicated by the dashed circles 312, 314, 316. The SE input may also beused to condition the scan register and logic circuitry 318 such that itoperates in a safe mode during the test. For example, it may conditionthe logic circuit such that no contention occurs between logic outputsduring the scan test. In test mode, SI provides the serial input to theinternal scan register, SO provides the serial output from the internalscan register, CS provides the control input protocol to cause theinternal scan register to capture response data from the logic circuitrythen shift data through the scan register from SI to SO to unload thecaptured response data and load the next stimulus data to be applied tothe logic circuitry.

FIG. 3B illustrates an IC or core 320 incorporating the scan test port(STP) 300 of FIG. 3A. For ICs, the SI, SO, and CS signals are typicallyshared with functional signal pins to save pin count while the SE signalis typically a dedicated IC pin so that it can be accessed to switch theshared pins between their functional and SI, SO, CS test modes. The CKsignal may be the ICs functional clock or it may be a dedicated testclock. For cores, the SE, SI, SO, CS, and CK signals may all bededicated for scan test access since cores typically do not suffer fromthe pin count problem that ICs do. The role of the SE signal on coresmay only be to condition the scan register and logic circuitry for thepreviously mentioned safe operation during the test, instead of beingused to switch inputs and outputs between functional and test mode asmentioned for the IC scan test port SI, SO, and CS signals.

FIG. 3C illustrates an IC or core 330 including both the STP 300 of FIG.3A and the TAP 100 of FIG. 1A. In FIG. 3C it is seen that the TAP andthe STP require different interface signals since their input and outputoperations are based on different serial interface protocols.

FIG. 4 illustrates a system IC 400 consisting of cores 1-N 402. Eachcore includes a TAP interface 100 and a STP interface 300. The core TAPsare serially connected, via a first scan path wiring bus 410, to allow atester to access the TAPs of embedded circuits in the cores, such as theembedded target circuits of FIGS. 1C-1F. The STPs are seriallyconnected, via a second scan path wiring bus 420, to allow a tester toaccess the STPs of embedded internal scan circuitry of the cores, suchas the scan circuitry of FIG. 3A. From FIG. 4 it is seen that the systemIC requires two test interfaces, one for the core TAPs and another forthe core STPs. Further, the IC requires two separate internal scan pathwiring buses, one scan path wiring bus 410 for the core TAPs and anotherscan path wiring bus 420 for the core STPs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1G illustrate the test architecture of conventional 1149.1TAPs.

FIG. 2 illustrates the state diagram of the TAP controller of FIG. 1A.

FIG. 3A illustrates a conventional internal scan test port interface toan internal scan register.

FIG. 3B illustrates an IC or core incorporating the scan test port (STP)of FIG. 3A.

FIG. 3C illustrates an IC or core including both the STP of FIG. 3A andthe TAP of FIG. 1A.

FIG. 4 illustrates a system IC consisting of cores 1-N.

FIG. 5A illustrates the structure of the present invention to utilize asingle IC test interface and a single internal scan path wiring bus toprovide access to the internal scan circuit 501 from either the TAP orSTP of FIG. 4.

FIG. 5B illustrates an individual scan cell used in FIG. 5A.

FIGS. 5C and 5D illustrate multiplexers used in FIG. 5A.

FIG. 6 is an embodiment of the present invention illustrating that thesource of the Lock Out signal could come from an additional IC pin orcore terminal, or from a register (R) or other circuit embedded withinthe system IC.

FIG. 7 illustrates an embodiment of the present invention for generatingthe Lock Out signal by the TAP itself and by using only the existingtest interface signals.

FIG. 8A illustrates the Lock Out circuit of FIG. 7.

FIG. 8B illustrates the operation of the Unlock state machine of FIG.8A.

FIG. 9 illustrates an embodiment of a system IC including cores 1-N thatuse the dual mode TAP/STP interface of the present invention.

FIG. 10A illustrates a test architecture according to another embodimentof the invention.

FIG. 10B illustrates a bypass register used in FIG. 10A.

FIGS. 10C and 10D illustrate multiplexers used in FIG. 10A.

FIG. 11 illustrates a second embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present invention.

FIG. 12A illustrates a test architecture according to another embodimentof the invention.

FIG. 12B illustrates a multiplexer used in FIG. 12A.

FIG. 13 illustrates a third embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present invention.

FIG. 14 illustrates an embodiment of the invention having a configurablescan circuit.

FIG. 15 illustrates a fourth embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present invention.

FIG. 16 illustrates another embodiment of the invention having aconfigurable scan circuit.

FIG. 17 illustrates a fifth embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present invention.

FIG. 18 illustrates a sixth embodiment of a system IC including cores1-N that use the dual mode TAP/STP interface of the present invention.

FIG. 19A illustrates a test architecture according to another embodimentof the invention.

FIG. 19B illustrates a scan cell used in FIG. 19A.

FIGS. 19C-19E illustrate multiplexers used in FIG. 19A.

FIG. 20A illustrates an example timing diagram of STP controlled scanoperations to the boundary scan register of FIG. 19A.

FIG. 20B illustrates a circuit for producing the STPUC signal used inFIG. 19D.

FIG. 20C illustrates boundary and internal scan cells.

FIG. 21 illustrates an IC containing cores having and TAP/STP interfacecoupled to a tester controlled scan path and a boundary scar register.

FIG. 22 illustrates an IC or core being tested via the TAP/STPinterface.

FIG. 23 illustrates an arrangement for connecting multiple TAP domainswithin an IC to a single scan path.

FIG. 24 illustrates a structure for connecting multiple TAP domainswithin an IC.

FIG. 25 illustrates circuitry for providing the TMS_(ICT), TMS_(CIT),and TMS_(CNT) signals in FIG. 24.

FIG. 26 illustrates circuitry for providing the TDI_(ICT), TDI_(CIT),and TDI_(CNT) signals in FIG. 24.

FIG. 27 illustrates circuitry for multiplexing the TDO_(ICT), TDO_(CIT),and TDO_(CNT) signals in FIG. 24 to the TDO output.

FIG. 28A illustrates the structure of the TLM of FIG. 24.

FIG. 28B illustrates the structure of instruction register of FIG. 28A.

FIG. 29 illustrates various arrangements of TAP domain connectionsduring 1149.1 instruction scan operations.

FIG. 30 illustrates that during 1149.1 data scan operations the TLM 2403of FIG. 24 is configured to simply form a connection path between theoutput of the selected TAP domain arrangement and the IC's TDO pin.

FIG. 31 illustrates how the structure of the TLM architecture of FIG. 24may be adapted to support TAP/STP domains instead of TAP domains.

FIGS. 32 and 33 represent the TAP/STP domain signal name substitutionfor the TAP domain signal names in the TMS gating circuitry and TDImultiplexing circuitry of the input circuitry of FIG. 31.

FIG. 34 represents the TAP/STP domain signal name substitution for theTAP domain signal names of the output circuitry of FIG. 31.

FIG. 35A illustrates the TLM of FIG. 31.

FIG. 35B illustrates the instruction register of FIG. 35A.

FIG. 36 illustrates various arrangements of TAP/STP domain connectionsduring 1149.1 TAP instruction scan operations using the TAP/STParchitecture of FIG. 31.

FIGS. 37 and 38 illustrate that during 1149.1 data scan operations theTLM 3103 is configured to form a connection path between the output ofthe selected TAP/STP domain arrangement and the IC's TDO/SO pin.

FIGS. 39 and 40 illustrate modified embodiments of the structure of FIG.31.

FIGS. 41-43 illustrate various arrangements of domain connections usingthe architecture of FIG. 40.

FIG. 44 illustrates process steps.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a method and structure for merging thecore TAPs and STPs into a single test interface and accessing the mergedTAP and STP test interface using a single internal scan path wiring bus.Further the present invention provides a method and structure forselectively accessing one or more merged TAP and STP test interfaces viaa single IC test pin interface and a single IC scan path wiring bus.

FIG. 5A illustrates the method and structure of the present invention toutilize a single IC test interface and a single internal scan pathwiring bus to provide access to the internal scan circuit 501 fromeither the TAP or STP of FIG. 4. In FIG. 5A, the internal scan circuit501 and TAP circuit 502 share a common SI and TDI test input connection(TDI/SI) and a common SO and TDO test output (TDO/SO) connection. Alsothe internal scan circuit 501 and TAP circuit 502 share a common TMS andCS test input connection (TMS/CS). Further, the TCK input is shared as aclock for both the internal scan circuit 501 and TAP circuit 502. Toenable the sharing of the test interface signals, an AND gate 503 isincluded in the TMS/CS signal path to the TAP to allow enabling the TAPor disabling the TAP. Also a 3-state buffer 506 is placed on the SOoutput of the scan circuit 501, and connection circuitry 505 is added asan interface to the scan circuitry. A signal called Lock Out is input tothe AND gate 503 and buffer 506 via OR gate 512. OR gate 512 inputs theLock Out signal and a SO enable signal from the TAP's instructionregister via bus 504. When Lock Out is high, the TAP is enabled toreceive and respond to the TMS/CS and the output of the 3-state buffer506 is disabled via OR gate 512. When Lock Out is low, the TAP isdisabled from receiving the TMS/CS signal. If the SO enable signal frombus 504 is low, the low on the Lock Out signal also enables the outputof the 3-state SO buffer 506, via OR gate 512.

In FIG. 5A, the internal scan register of the internal scan circuit 501remains a data register within the TAP data registers section, asevidenced by the serial input 101, serial output 104, and control 511connections to the TAP 502. Therefore, scan circuit 501 remainsconventionally accessible as one of the data registers within the TAP'sdata register section, as previously shown and described in regard toFIGS. 1A and 1C. In general the present invention maintains TAP accessto any data register which is also rendered accessible by the STPinterface, including but not limited to all other data registers shownin FIGS. 1A and 1D-1G. Thus the present invention provides a dual modetest access port for accessing data registers using either the TAP orSTP interfaces.

FIG. 5A illustrates the method and structure of the present invention toutilize a single IC test interface and a single internal scan pathwiring bus to provide access to the internal scan circuit 501 fromeither the TAP 100 or STP 300 of FIG. 4. In FIG. 5A, the internal scancircuit 501 and TAP circuit 502 share a common SI and TDI test inputconnection (TDI/SI) and a common SO and TDO test output (TDO/SO)connection. Also the internal scan circuit 501 and TAP circuit 502 sharea common TMS and CS test input connection (TMS/CS). Further, the TCKinput is shared as a clock for both the internal scan circuit 501 andTAP circuit 502. To enable the sharing of the test interface signals, anAND gate 503 is included in the TMS/CS signal path to the TAP to allowenabling the TAP or disabling the TAP. Also a 3-state buffer 506 isplaced on the SO output of the scan circuit 501, and connectioncircuitry 505 is added as an interface to the scan circuitry. A signalcalled Lock Out is input to the AND gate 503 and buffer 506 via OR gate512. OR gate 512 inputs the Lock Out signal and a SO enable signal fromthe TAP's instruction register 112 via bus 504. When Lock Out is high,the TAP is enabled to receive and respond to the TMS/CS and the outputof the 3-state buffer 506 is disabled via OR gate 512. When Lock Out islow, the TAP is disabled from receiving the TMS/CS signal. If the SOenable signal from bus 504 is low, the low on the Lock Out signal alsoenables the output of the 3-state SO buffer 506, via OR gate 512.

In FIG. 5A, the internal scan register 310 of the internal scan circuit501 remains a data register within the TAP data registers section, asevidenced by the serial input 101, serial output 104, and control 511connections to the TAP 502. Therefore, scan circuit 501 remainsconventionally accessible as one of the data registers within the TAP'sdata register section 114, as previously shown and described in regardto FIGS. 1A and 1C. In general the present invention maintains TAPaccess to any data register which is also rendered accessible by the STPinterface, including but not limited to all other data registers shownin FIGS. 1A and 1D-1G. Thus the present invention provides a dual modetest access port for accessing data registers using either the TAP orSTP interfaces.

Referring also to FIG. 44, assuming the TAP 502 is initially enabled4400 but that access to the internal scan circuit 501 is desired usingthe STP interface, the following sequence would occur. The TAP would beaccessed to load a scan test instruction into its instruction register4402. The scan test instruction would be defined according to thepresent invention to output control on bus 504 of the present inventionto connection circuitry 505 and OR gate 512 of the present invention. Asseen in FIG. 5A, one of the instruction control output signals thatpasses through connection circuit 505 to be input to the scan circuit501 is the SE input. As mentioned in regard to FIG. 3A, the SE input isconventionally input using an IC pin. However, the present inventiongenerates the SE signal internally using an instruction which eliminatesthe need for a dedicated IC pin to input the SE signal. The instructioncontrol on bus 504 may also be output to other circuits not shown inFIG. 5A to condition them for the pending internal scan test operation.The instruction control output occurs during the Update-IR state ofFIGS. 2 and 4404 of FIG. 44. Simultaneous with the instruction controloutput, the Lock Out signal transitions from a logic high to a logic low4406. AND gate 503 passes the Lock Out logic low to the TAP's TMS inputand OR gate 512 passes the Lock Out logic low to the control input ofthe SO buffer 506. The TAP controller responds to the logic low on theTMS input to transition from the Update-IR state to the Run Test/Idlestate, as seen in FIG. 2. Also the logic low on the Lock Out signal andthe logic low on the SO enable signal to OR gate 512 enables the SObuffer 506 to drive the TDO/SO output. Note that if the instructionloaded into the instruction register does not set the SO enable signalto a logic low, the SO output buffer 506 would not be enabled by a thelogic low on Lock Out, since the output of OR gate 512 would remain at alogic high state.

After the above sequence is performed, the TAP is disabled by the LockOut signal to its Run Test/Idle state (FIG. 2). While the TAP is forced,by the Lock Out signal, to remain in the Run Test/Idle state, the TMS/CSsignal can be used as the CS signal of FIG. 3A to control the captureand shift operations of the scan circuit 501. While the TAP is disabled,its TDO output buffer is disabled to allow the enabled SO buffer 506 todrive out on the TDO/SO output. In preparation for an STP controlledscan test, the TCK signal is connected to the scan circuit's CK inputusing, for example, a multiplexer 520 as shown in FIG. 5C, and theTMS/CS signal is connected to the scan circuit's CS input using, forexample, a multiplexer 540 as shown in FIG. 5D. The CKSEL and CSSELcontrol inputs to the multiplexers 520, 540 of 5C and 5D come from theinstruction output control on bus 504. The CK and CS outputs from themultiplexers of 5C and 5D are connected to the individual scan cells ofthe internal scan register of scan circuit 501, such as scan cell 560 ofmultiplexer 562 and flip-flop 564 shown in FIG. 5B. The internal scanregister comprises multiple ones of the FIG. 5B scan cells 560 connectedserially between their serial input (SI) and serial output (SO). The CKand CS multiplexing circuitry reside in connection circuitry 505. TheFCK input to connection circuitry 505 is the functional clock source.During the STP controlled scan test operation, scan circuit 501 receivesthe TMS/CS input as the CS input of FIG. 3A and the TCK input as the CKinput of FIG. 3A to capture data and shift data from TDI/SI to TDO/SO ofFIG. 5A. Thus, when setup by the sequence described above, the scancircuit 501 is rendered scan testable via the STP interface as describedpreviously in regard to FIG. 3A.

FIG. 6 is provided to simply illustrate that the source of the Lock Outsignal could come from an additional IC pin or core terminal 604, orfrom a register (R) 602 or other circuit embedded within the system IC.

FIG. 7 illustrates a method and structure for generating the Lock Outsignal by the TAP itself and by using only the existing test interfacesignals (TDI/SI, TMS/CS, TCK, TRST, and TDO/SO). The advantage ofproducing the Lock Out signal using only the pre-existing test interfacesignals is that no additional pin/terminal is required on the IC/core,and that testers that drive IC TAP interfaces today can be used to setthe Lock Out signal without having to provide an additional hardwaretest interface signal to drive the Lock Out pin/terminal signal of FIG.6. As seen in FIG. 7, the modification to include a TAP generated LockOut signal involves: (1) providing a TAP Lock circuit 508, (2) providingand connecting a Lock Input signal 507 to the TAP Lock circuit 508 frominstruction register output bus 504, (3) providing an instruction toproduce the Lock Input signal output onto bus 504, (4) connecting theUpdate-IR signal output from the TAP controller to the Lock Out circuit508, (5) connecting the TCK input to the Lock Out circuit 508, (6)connecting the TMS/CS input to the Lock Out circuit 508, and (7)connecting the TRST input to the Lock Out circuit 508. The Lock Inputsignal 507 is output from the instruction register such that the TAPcontroller Update-IR signal may clock it into the Lock Out circuit 508during the Update-IR state of FIG. 2, i.e. the Lock Input signal 507 isoutput from the instruction register prior to the occurrence of the TAPcontroller's Update-IR signal that occurs at the end of each instructionscan operation.

FIG. 8A illustrates in detail the Lock Out circuit 508. The Lock Outcircuit consists of a D-FF 801 for receiving the Lock In signal 507 atits data input, the Update-IR signal at its clock input, and a resetinput via AND gate 804. The Lock Out circuit also includes an Unlockstate machine 803. The Unlock state machine receives TCK as a clockinput, TMS/CS as a data input, TRST as reset input, and the data outputof D-FF 801 as an enable input. The Unlock state machine outputs anUnlock signal to the reset input of the D-FF 801, via AND gate 804. TRSTis also input to the reset input of D-FF 801 via AND gate 804. Inresponse to the Update-IR signal from the TAP controller, the D-FFoutputs the state of the Lock In input to the Unlock state machine andto inverter 802 which outputs the Lock Out output signal. As long as thedata output from D-FF 801 is low, the Unlock state machine is disabledand the Lock Out output from inverter 802 is high. While Lock Out ishigh, the TAP is enabled to respond to the TMS/CS input via AND gate503, and the SO buffer 506 is disabled as previously described. When aninstruction is loaded into the TAP's instruction register to enable anSTP controlled scan test operation, the Lock Input will be set high suchthat, in response to the Update-IR signal, the data output of the D-FFgoes high. A high on the data output of the D-FF enables the Unlockstate machine and sets Lock Out from inverter 802 low. A low on Lock Outdisables the TAP to the Run Test/Idle state and the enables the SObuffer 506 as previously described. Also the instruction outputs controlvia bus 504 to connection circuit 505 to input the SE signal to scancircuit 501 and to form appropriate CS and CK connections to scancircuit 501 for the STP controlled scan test operation, and to set theSO enable signal to OR gate 512 low, again as previously described.

While Lock Out is low, the Unlock state machine is enabled to monitorthe state of the TMS/CS signal during each TCK period. During the STPcontrolled test operation, the TMS/CS signal input to scan circuit 501goes low to capture data then goes high to shift data from TDI/SI toTDO/SO. The number of times the Unlock state machine detects a low onTMS/CS is therefore only during the times when the scan circuitry 501 isperforming a capture operation. Conventionally, the STP operates tocapture data using one TCK period, then shifts data using multiple TCKperiods. The Unlock state machine exploits this conventional STP captureand shift timing to devise a simple method of escaping from the STPcontrolled mode to re-enter the TAP controlled mode. The operation ofthe Unlock state machine and its escape sequence is best understood byinspection of the Unlock state diagram of FIG. 8B.

As seen in FIG. 8B, the Unlock state machine comprises Idle 1 820, Idle2 822, Sequence 1-3 824, 826, 828, and Unlock TAP 830 states. When firstenabled by the data output of D-FF 801 going high, the Unlock statemachine will be in the Idle 1 state and will remain in the Idle 1 statewhile TMS/CS is low. Holding TMS/CS low to maintain the Idle 1 statewhen the Unlock state machine is first enabled, provides time for thetest interface and architecture to switch from TAP controlled operationto STP controlled operation. For example, during the Update-IR statethat enables the Unlock state machine in the Idle 1 state, the CKSEL andCSSEL control signals are input to the CK and CS multiplexers of FIGS.5C and 5D to couple CK to TCK and CS to TMS/CS, and the Lock Out signalenables SO buffer 506. By holding TMS/CS low to remain in the Idle 1state for a certain number of TCKs, the CK and CS multiplexers are giventime to switch, the scan circuit 501 is given time to respond to the CKand CS switch, and the SO buffer 506 is given time to become enabled.After the CK and CS switch and SO buffer enable time, the scan circuit501 will operate in the capture mode since it will be receiving CKinputs (via TCK) while the CS input is low (via TMS/CS being low).

Applying a high level on TMS/CS will initiate the first shift operationthrough scan circuit 501 from TDI/SI to TDO/SO and cause the Unlockstate machine to transition from the Idle 1 state to the Idle 2 state.The Idle 2 state is maintained while TMS/CS is high to complete thefirst shift operation. At the end of the shift operation, a low level isapplied to TMS/CS to initiate a capture operation and to cause theUnlock state machine to transition from the Idle 2 state to the Sequence1 state. At the end of the capture operation, a high level is applied toTMS/CS to initiate the second shift operation and to transition theUnlock state machine from the Sequence 1 state to the Idle 2 state. Thehigh on TMS/CS maintains the second shift operation until the nextcapture operation is required, at which time a low level will be appliedon TMS/CS. The above shift/capture operation and corresponding Idle2/Sequence 1 state sequence repeats until the STP controlled test ofscan circuit 501 has been completed. At the end of the last shiftoperation of the STP controlled test, a low level is applied andmaintained on TMS/CS which causes the Unlock state machine to transitionfrom the Idle 2 state, through the Sequence 1-3 state, through theUnlock TAP state, to re-enter the Idle 1 state. Passing through theUnlock TAP state, the Unlock state machine outputs an Unlock signal tothe reset input of D-FF 801, via AND gate 804. In response to the Unlocksignal, the data output of the D-FF goes low, which disables the Unlockstate machine to its Idle 1 state and sets the Lock Out from inverter802 high. When Lock Out goes high, the SO buffer 506 is disabled and theTAP controller is once again enabled to respond to the TMS/CS input viaAND gate 503 to provide control of the test architecture. The enabledTAP controller will remain in the Run Test/Idle state if TMS/CS remainslow, or, as seen in FIG. 2, it may transition from the Run Test/Idlestate to perform a data register scan operation, an instruction registerscan operation, or enter the Test Logic Reset state.

In some variances of STP controlled testing, back to back captureoperations may occur between shift operations to support delay testingof the scan circuit 501. The Unlock state machine is designed to allowfor this back to back capture (i.e. two consecutive lows on TMS/CS)possibility as seen in state transitions from Idle 2 to Sequence 1 toSequence 2, and back to Idle 2. In fact, as seen in the state diagram,the Unlock state machine can handle up to three back to back capture(i.e. three consecutive lows on TMS/CS) operations without Unlocking theTAP, as seen by state transitions from Idle 2 to Sequence 1 to Sequence2 to Sequence 3, and back to Idle 2. In general, Unlock state machinesare designed to comprehend the total number of consecutive TMS/CS lowsignals required to perform any given STP controlled test operation. TheSTP controlled test operation will be maintained as long as the numberof consecutive TMS/CS low signals is less than or equal to that totalnumber. If the number of consecutive TMS/CS low signals exceeds thattotal number, the Unlock state machine will disable STP control andreinstate TAP control of the test architecture, as described above.

FIG. 9 illustrates a system IC 900 including cores 1-N 920, 922, 924that use the dual mode TAP/STP interface 926 of the present invention.In this example, each TAP/STP interface includes a TAP lock circuit 508of FIGS. 7, 8A, and 8B, so only the IEEE 1149.1 standard TDI, TDO, TMS,TCK, and TRST signal pins are required on the IC for selecting the TAPor STP mode of the TAP/STP interface, i.e. the Lock Out signal pin ofFIG. 6 is not required. A first advantage of the present invention isthat the system IC of FIG. 9 only has to provide a single internal scanpath wiring bus 910 to the cores for performing both TAP controlled andSTP controlled operations. In contrast, the system IC of FIG. 4 had toprovide two internal scan path wiring buses 410 and 420 to the cores,one for the TAP and another for the STP. A second advantage of thepresent invention is that the tester connected to the system IC of FIG.9 can selectively perform either TAP or STP controlled operations usingthe same standard IC test pins defined in the IEEE 1149.1 standard, i.e.TDI, TDO, TMS, TCK, and TRST. In contrast, a tester connected to thesystem IC of FIG. 4 had to provide two separate IC test pin interfacesto the IC, one for the TAP and another for the STP.

At power up of the system IC of FIG. 9, all core TAP/STP interfacespreferably default to the TAP control mode so that the core TAPs can beaccessed for scanning in instructions to setup test, emulation,programming, or other TAP controlled operations. When STP controlledscan testing is required in all the cores, a TAP instruction scan willbe performed to load an STP enable instruction into each core's TAPinstruction register, as described in regard to FIGS. 5A, 6A, 7, and 8A.Once the instruction is updated during the Update-IR state of FIG. 2,all core TAP/STP interfaces switch from the TAP control mode to the STPcontrol mode. Assuming each core has an internal scan circuit 501 asdescribed in FIGS. 5-7, a tester may perform scan testing on all thedaisy-chained internal scan circuits 501 of cores 1-N via the singletest pin interface and single scan path wiring bus 910. At the end ofthe STP controlled test operation, TAP control of the core TAP/STPinterfaces can be reinstated by setting the TMS/CS signal to a statethat will disable the TAP lock circuits 508 to their Idle 2 state, asdescribed in FIGS. 8A and 8B.

In FIG. 9, a dotted line connection 904 is shown formed between thecores to illustrate another example implementation of the presentinvention whereby a single TAP lock circuit of one core (Corel) is usedto provide Lock Out signals to other cores (Cores 2-N) which do notthemselves have TAP lock circuits. In this example, the TAP lock circuitof Core 1 is equipped with an output terminal 901 for outputting theLock Out signal to connection 904 and Cores 2-N are equipped with inputterminals 902 and 903 for inputting the Lock Out signal from Core 1.Core 1 would utilize the FIG. 7 TAP/STP interface which includes the TAPlock circuit. Cores 2-N would utilize the FIG. 6 TAP/STP interface whichdoes not include the TAP lock circuit, but rather inputs the Lock Outsignal via a core terminal. The operation of this alternate realizationof the present invention to switch between TAP and STP controlled modesis the same as previously described. The use of a single TAP lockcircuit to generate the Lock out signal to a plurality of TAP/STPinterfaces, as shown in FIG. 9, should be understood to be an alternatemethod of implementing the present invention in all examples describedherein. In some implementations, the use of one TAP lock circuit in oneTAP/STP interface to generate the Lock out signal to other TAP/STPinterfaces as shown in FIG. 9 may be preferred since it eliminates theneed for each TAP/STP interface to have its own TAP lock circuit.

As mentioned in the FIG. 9 STP controlled test operation above, allcores 1-N were assumed to have a scan circuit 501 so that all the scancircuits 501 could be daisy-chained onto the scan path wiring bus 910and tested at the same time. However, not all the cores may have a scancircuit 501. Therefore a method and structure is needed to allow STPcontrolled daisy-chaining of the core TAP/STP interfaces onto scan pathwiring bus 910 when all the cores do not have scan circuits 501, or whentesting of only a selected one or more of the scan circuits 501 isdesired. The following description of FIGS. 10A-D and 11 provides amethod and structure of the present invention for selecting the bypassregister of the TAP/STP interfaces to be inserted into the scan pathwiring bus 901 to provide an alternate daisy-chain arrangement betweenthe cores.

FIG. 10A illustrates a test architecture similar to that described inregard to FIG. 7. The difference between the test architecture of FIG.10A and FIG. 7 is that the TAP's bypass register 1001 of FIG. 1A hasbeen selected for STP controlled scanning instead of the scan circuit501 of FIG. 7. An example bypass register is shown in FIG. 10B. Theserial input to multiplexer 1020 of the bypass register 1001 isconnected to TDI/SI via connection 101. The serial output of flip-flop1022 of the bypass register is connected to the TAP data registerssection via connection 108 to maintain conventional TAP controlledaccess as described in regard to scan circuit 501 of FIG. 5A. The serialoutput of the bypass register is also selectively connectable to theTDO/SO output via SO buffer 1005. Connection circuitry 1004 is providedfor connecting the TAP controller's Clock-DR and Capture-DR to thebypass registers CK and CS inputs during TAP controlled operation, orfor connecting the bypass register CK and CS inputs to TCK and TMS/CSduring STP controlled operation. An example CK multiplexer 1024 is shownin FIG. 10C, and an example CS multiplexer 1026 is shown in FIG. 10D.Both multiplexers reside in connection circuit 1004 and both receivebypass register CK and CS selection signals CKSEL and CSSEL from the TAPinstruction register via bus 504.

The process for selecting the bypass register between TDI/SI and TDO/SOand switching the TAP/STP interface into the STP controlled mode issimilar to that described for selecting the scan circuit 501 of FIGS.5-7. While in the TAP controlled mode, a bypass instruction is scannedinto and updated from the instruction register. The outputs from theinstruction register are input to the TAP lock circuit 508, connectioncircuit 1004, and OR gate 1006, via bus 504. In response to the signalsfrom bus 504, the TAP lock circuit outputs a low on Lock Out whichdisables the TAP and enables SO output buffer 1005 via OR gate 1006. TheLock Out signal is allowed to pass through OR gate 1006 since the bypassregister SO enable signal to OR gate 106 from the instruction registeris set low. Also, in response to the signals from bus 504, connectioncircuitry 1004 connects TMS/CS to the bypass register's CS input and TCKto bypass register's CK input. It should be noted that the SO buffer1005, OR gate 1006, and connection circuitry 1004 is separate from theSO buffer 506, OR gate 512, and connection circuitry 505. Also thebypass instruction control signals to connection circuitry 1004, SObuffer 1005, and OR gate 1006 is separate from the scan test instructioncontrol signals to connection circuitry 505, SO buffer 506, and OR gate512. In general this is true for all data registers (i.e. internal scan,bypass, boundary scan, ISP, and ICE data registers of FIG. 1A) that arerequired to be individually connected between TDI/SI and TDO/SO andoperated in the STP control mode. When the bypass SO buffer 1005 isenabled to drive out on TDO/SO, all other SO buffers (for example thescan circuit SO buffer 506 of FIG. 7) will be disabled to avoidcontention during STP controlled testing.

FIG. 11 illustrates an example IC 1100 containing cores 1-N 1102, 1104,1106. In this example, all the TAP/STP core interfaces have beenswitched to the STP controlled mode. Cores 1 and 3-N have had theirbypass registers 1001 connected between their TDI/SI and TDO/SOterminals, as described in the process above. Core 2 has had its scancircuit 501 connected between its TDI/SI and TDO/SO terminals, asdescribed in regard to FIGS. 5-7. FIG. 11 illustrates an example of howto daisy-chain cores onto scan path wiring bus 910 to where cores notbeing tested (Cores 1, 3-N) select their bypass registers 1001 to be inthe daisy-chain scan path 910 while cores being tested (Core 2) selecttheir scan circuit 501 to be in the daisy-chain scan path 910. Duringthe STP controlled capture operation the bypass registers 1001 of Cores1 and 3-N capture a logic low, as shown in FIG. 10B, and the scancircuit 501 of Core 2 captures test response data. During the STPcontrolled shift operation the bypass registers 1001 of Cores 1 and 3-Nshift data along the scan path 910 from the their TDI/SI input to TDO/SOoutput terminals, as shown in FIG. 10B, and the scan circuit 501 of Core2 shifts data along scan path 910 from its TDI/SI input to TDO/SO outputterminals.

FIG. 12A illustrates another example configuration of the presentinvention whereby the serial input and serial output of scan circuit 501are multiplexed to a test pattern source and a test pattern destination,respectively. The test pattern source 1208 could be internally generatedby a circuit within the IC, such as a linear feedback shift register, orit could be externally input from a tester via an IC pin. The testpattern destination 1209 could be internally processed by a circuitwithin the IC, such as a signature analyzer, or it could be externallyoutput to a tester via an IC pin. The TAP/STP interface is similar tothat described in FIGS. 5-7. The key differences between the TAP/STPinterface of FIG. 12A and the TAP/STP interfaces of FIGS. 5-7 include;(1) multiplexer 1201 is provided to selectively connect the serial inputof scan circuit 501 to either source 1208 or TDI/SI 101, (2) multiplexer1203 1202 is provided to selectively connect the serial output of scancircuit 501 to destination 1209 in substitution of functional signal1203, (3) the FCK signal 1206 is made available at a core terminal or ICpin to serve as the CK input to scan circuit 501, (4) a capture shiftsignal source (CSs) 1207 is provided and made available at a coreterminal or IC pin to serve as the CS input to scan circuit 501, and (5)a source/destination test instruction is provided that, when shiftedinto and updated from the TAP instruction register, provides control onbus 504 to multiplexers 1201 and 1202 and to connection circuitry 1210,to connect scan circuit 501 to the source, destination, FCK, and CSssignals. While a multiplexer 1202 is shown for connecting the serialoutput of scan circuit 501 to the destination 1209, in substitution of afunctional signal 1203, the serial output may be coupled to thedestination using a source/destination instruction controlledcontrolling a 3-state buffer as well. For cores, the serial output fromscan circuit 501 may have a dedicated output terminal for connecting todestination 1209.

Connection circuitry 1210 comprises a CK multiplexer like that shown inFIG. 5C to allow the FCK 1206 signal to be coupled to the scan circuit's501 CK input in response to the source/destination test instructionoutput on bus 504. The connection circuitry 1210 also includes the CSmultiplexer 1220 of FIG. 12B, to allow CSs 1207 to be coupled to thescan circuits CS input, in response the source/destination testinstruction output on bus 504. In addition to the test source anddestination test mode configuration described above, the TAP/STPinterface of FIG. 12A maintains the previously described TAP and STPcontrolled test modes to scan circuit 501. Also it is should beunderstood that the new source and destination test mode operatesindependent of the TAP/STP interface, once the source/destination testinstruction has been loaded. Further, the TAP/STP interface may beplaced in either the TAP controlled or STP controlled mode by thesource/destination test instruction without effecting the operation ofthe source and destination tests. Indeed, two source/destination testinstructions may be used. A first source/destination test instructionmay configure scan circuit 501 for source and destination testing asdescribed above and leave the TAP/STP interface in the TAP controlledmode. A second source/destination test instructions may configure scancircuit 501 for source and destination testing as described above andplace the TAP/STP interface into the STP controlled mode.

FIG. 13 illustrates an example IC 1300 containing cores 1-N 1302, 1304,1306 having TAP/STP interfaces coupled to scan path 910. Each coreincludes the source and destination test mode described in regard toFIG. 12A. When the source/destination test instruction is loaded intothe cores, each core connects its source input 1208 to a respectiveinternal or external source 1301, 1303, 1305, connects its destinationoutput 1209 to a respective internal or external destination 1302, 1304,1306, connects its CSs input 1207 to a respective internal or externalCSs 1307, 1309, 1311, and connects its FCK input 1206 to a respectiveinternal or external FCK 1308, 1310, 1312. Once the source anddestination configuration is made, the scan circuits 501 of the cores1-N can be tested. During the test, the core's CSs 1207 and FCK 1206inputs are operated to capture data and shift data through the scancircuits 501 from the source inputs 1208 to the destination outputs1209. Separate CSs 1307, 1309, 1311, FCKs 1308, 1310, 1312, sources1301, 1303, 1305, and destinations 1302, 1304, 1306 may be used for eachcore for asynchronous core testing, or alternately each core may beinterfaced to the same CSs and FCK to allow communication between thecore 1-N sources and destinations to occur synchronously. While sourceand destination testing occurs, the core's TAP/STP interfaces may beaccessed via scan path 910 without interfering with the sourcedestination testing. Also the core TAP/STP interfaces may be accessedusing either TAP control or STP control.

FIG. 14 illustrates another example configuration of the presentinvention whereby a configurable scan circuit 1401 is substituted forscan circuit 501. The logic circuitry of scan circuit 1401 can be testedin a first configuration where the scan circuit 1401 scan path isconfigured into a single scan register, or in a second configurationwhere the scan circuit 1401 scan path is configured into separateparallel scan registers 1-N 1440,1442. When placed in the firstconfiguration, the single scan register can be coupled between TDI/SIand TDO/SO and tested using either the TAP or STP as previouslydescribed for scan circuit 501. When placed in the second configuration,the serial inputs of the separate parallel scan registers 1-N arecoupled to parallel sources 1-N 1409 via multiplexers 1402-1403, and theserial outputs of the separate parallel scan registers 1-N are coupledto parallel destinations 1-N 1408 via multiplexers 1405-1406. Thesources 1409 and destinations 1408 can be internally or externallyprovided, as described in regard to FIG. 12A.

The key differences between the TAP/STP interface of FIG. 14 and TAP/STPinterfaces of FIGS. 5-7 and 12A include; (1) multiplexer 1402 isprovided to selectively connect the serial input of parallel scanregister N 1440 to either source N or the serial output of parallel scanregister N−1, or in this example where N=2, to the serial output ofparallel scan register 1 1442, (2) multiplexer 1403 is provided toselectively connect the serial input of parallel scan register 1 1442 toeither source 1 or TDI/SI 101, (3) multiplexer 1405 is provided toselectively connect the serial output of parallel scan register N 1440to destination N in substitution of functional a signal 1410, (4)multiplexer 1406 is provided to selectively connect the serial output ofparallel scan register 1 1442 to destination 1 in substitution of afunctional signal 1411, (5) a serial test instruction is provided that,when shifted into and updated from the TAP instruction register,provides control on bus 504 to multiplexers 1402-1403 and 1405-1406 toserially connect parallel scan registers 1-N 1440,1442 into a singlescan path for TAP or STP access via TDI/SI and TDO/SO, (6) a paralleltest instruction is provided that, when shifted into and updated fromthe TAP instruction register, provides control on bus 504 tomultiplexers 1402-1403 and 1405-1406 to connect the parallel scanregisters 1-N 1440,1442 to sources 1-N and destinations 1-N for TAP orSTP controlled access via sources 1-N and destinations 1-N.

In response to either of the above serial or parallel test instructions,connection circuit 505 receives control on bus 504 to operate the scanregisters of scan circuit 1401 in either the TAP or STP controlled mode,as previously described. As with the source/destination test instructionof FIG. 12A, both TAP and STP controlled versions of the serial testinstruction and a parallel test instruction may be provided to allow theserial and parallel configurations of scan circuit 1401 to be controlledby either the TAP or STP.

FIG. 15 illustrates an example IC 1500 containing cores 1-N 1503, 1504,1506 having TAP/STP interfaces coupled to scan path 910. Each coreincludes the serial and parallel scan test access modes to scan circuit1401 as described in regard to FIG. 14. When the serial test instructionis loaded into the cores, the scan circuits 1401 are accessed and testedusing only the scan path 910 signals, and using either TAP or STPcontrol. The operation of the serial test instruction in FIG. 15 to testdaisy-chained scan circuits 1401 is similar in operation to the scantest instruction of FIG. 9 to test daisy-chained scan circuits 501. Whenthe parallel test instruction is loaded into the cores, the scancircuits 1401 of cores 1-N are coupled to source 1-N inputs 1409 anddestination 1-N output 1408. As seen in FIG. 15, the source 1-N input ofCore 1 is connected to a source 1501 which can be either internally orexternally provided. The destination 1-N output of Core 1 is connectedto the source 1-N input of Core 2. The destination 1-N output of Core 2is connected to the source 1-N input of Core N. The destination 1-Noutput of Core N is connected to destination 1502 which can be eitherinternally or externally provided. In this arrangement, the scancircuits 1401 of cores 1-N are seen to be daisy-chained on a parallelscan bus beginning at source 1501 and ending a destination 1502. TheTMS/CS and TCK input signals to the core TAP/STP interfaces from scanpath 910 are used to control the capture of data and the shifting ofdata through the daisy-chained scan circuits 1401 from source 1501 todestination 1502. The capturing and shifting of data through thedaisy-chained scan circuits 1401 can be either TAP or STP controlled.

FIG. 16 illustrates another example configuration of the presentinvention whereby the configurable scan circuit 1401 FIG. 14 is madecontrollable from the FCK 1206 and CSs 1207 inputs to connectioncircuitry 1210 as described earlier in regard to FIG. 12A. The FIG. 16example maintains the serial and parallel test instruction modesdescribed in regard to FIGS. 14 and 15. Additionally, the FIG. 16example provides a parallel source/destination test instruction thatenables the FCK and CSs inputs to control the capture and shiftoperations of scan circuit 1401. The parallel source/destinationinstruction is similar to the source/destination instruction of the FIG.12A example. The key difference is that scan circuit 1401 is connectedto parallel source 1-N inputs 1409 and parallel destination 1-N outputs1408, as opposed to the scan circuit 501 being connected to a singlesource input 1208 and a single source output 1209.

FIG. 17 illustrates an example IC 1700 containing cores 1-N 1708, 1710,1712 having TAP/STP it, interfaces coupled to scan path 910. Each coreincludes the parallel source and destination test mode described inregard to FIG. 16. When the parallel source/destination test instructionis loaded into the cores, each core connects its parallel source input1409 to a respective internal or external parallel source 1701, 1703,1705, connects its parallel destination output 1408 to a respectiveinternal or external parallel destination 1702, 1704, 1706, connects itsCSs input 1207 to a respective internal or external CSs 1307, 1309,1311, and connects its FCK input 1206 to a respective internal orexternal FCK 1308, 1310, 1312. Once the parallel source and destinationconfiguration is made, the scan circuits 1401 of the cores 1-N can betested. During the test, the core's CSs 1207 and FCK 1206 inputs areoperated to capture data and shift data through the scan circuits 1401from the source inputs 1409 to the destination outputs 1408. SeparateCSs 1307, 1309, 1311, FCKs 1308, 1310, 1312, sources 1701, 1703, 1705,and destinations 1702, 1704, 1706 may be used for each core forasynchronous core testing, or alternately each core may be interfaced tothe same CSs and FCK to allow communication between the core 1-N sourcesand destinations to occur synchronously. While parallel source anddestination testing occurs, the core's TAP/STP interfaces may beaccessed via scan path 910 without interfering with the parallel sourcedestination testing. Also the core TAP/STP interfaces may be accessedusing either TAP control or STP control.

FIG. 18 illustrates an example of how the present invention may be usedto simultaneously enable and execute different types of testing ondifferent cores 1-N 1802, 1804, 1806 within an IC 1800. Core 1 has beenloaded with the source/destination test instruction previously describedin regard to FIGS. 12A and 13. Core 2 has been loaded with the scan testinstruction as previously described in regard to FIGS. 5-9. Cores 3-Nhave been loaded with the parallel source/destination test instructiondescribed in regard to FIGS. 16-17. To setup the test, a single TAPcontrolled instruction scan may be performed to load each of the abovementioned test instructions into the TAP/STP interfaces of each core1-N. Following the instruction scan, Core 1 is configured for source anddestination testing as described in FIGS. 12A and 13, Core 2 isconfigured for scan testing as described in regard to FIGS. 5-9, andCores 3-N is configured for parallel source and destination testing asdescribed in regard to FIGS. 16-17.

As seen in FIG. 18, the source destination test instruction loaded intoCore 1 selects the bypass register 1001 to be coupled between Core 1'sTDI/SI and TDO/SO terminals. Also the parallel source destination testinstruction loaded into Cores 3-N selects the bypass register 1001 to becoupled between each of the Core 3-N TDI/SI and TDO/SO terminals. Thebypass registers 1001 are selected to allow access to and testing ofscan circuit 501 of Core 2 via scan path 910, while Cores 1 and 3-N arebeing tested using the described source and destinations test methods.To enable access to Core 2's scan circuit 501, the source destinationtest instruction loaded into Core 1 and the parallel source destinationinstructions loaded into Cores 3-N are designed to not only configureCores 1 and 3-N for their respective source and destination testing, butalso to select the bypass register 1001 between TDI/SI and TDO/SO.Additionally, the TAP/STP interfaces of cores 1-N may be selectively setby the instructions to operate the TAP/STP interfaces in either the TAPor STP controlled mode.

If TAP/STP interfaces are set to operate in the TAP controlled mode, thebypass registers of Cores 1 and 3-N and the scan circuit 501 of Core 2will operate on scan path 910 according to the TAP state machine statediagram of FIG. 2. If set to operate in the STP controlled mode, thebypass registers of Cores 1 and 3-N and the scan circuit 501 of Core 2will operate on scan path 910 according to the STP capture and shiftscan protocol. The TAP or STP controlled testing of scan circuit 501 ofCore 2 does not interfere with the source and destination testing ofCores 1 and 3-N because the signals used for the source and destinationtesting (i.e. CSs 1207, FCK 1206, source 1208, destination 1209, source1-N 1407 and destination 1-N 1408) are separate from the scan path 910signals (i.e. TDI/SI, TMS/CS, TCK, TRST, and TDO/SO). Therefore thecores of FIG. 18 may be tested in parallel using the three differenttest methods illustrated and described. In general, FIG. 18 illustrateshow the TAP/STP interface of the present invention and the instructionsdefined for the TAP/STP interfaces may be used to allow scan path 910 tobe used for TAP or STP controlled testing simultaneous with testingperformed by signals separate from the TAP/STP interface signals.

FIG. 19A illustrates a test architecture 1900 similar to that describedin regard to FIG. 7. The difference between the test architectures ofFIG. 19A and FIG. 7 is that the TAP's boundary scan register 1901 ofFIGS. 1A and 1F has been selected for STP controlled scanning instead ofthe scan circuit 501 of FIG. 7. An example boundary scan cell is shownin FIG. 19B. The boundary scan cell 1920 receives a functional input(FI), a serial input (SI) input, CS input, CK input, update control (UC)input, and a mode input. The boundary scan cell outputs a functionaloutput (FO) and a serial output (SO). The mode control input comes fromthe TAP instruction register and allows coupling FI to FO duringfunctional operation, or coupling FO to the output of the update FF 1904during test operation. The multiplexer and FF combination 1905 providesfor capturing FI data and shifting data from SI to SO in response to theCS and CK signals. Update FF 1904 loads data from FF 1905 in response tothe UC signal. The boundary scan register comprises multiple ones of theboundary scan cells of FIG. 19B connected serially between their SI andSO. All the boundary scan cells are commonly connected to the mode, CS,CK, and UC signals. The serial input of the boundary scan register 1901is connected to TDI/SI via connection 101. The serial output of theboundary scan register from MUX 1921 is connected to the TAP dataregisters section via connection 107 to maintain conventional TAPcontrolled access to the boundary scan register, as mentioned in regardto FIG. 5A. The serial output of the boundary scan register is alsoselectively connectable to the TDO/SO output via SO buffer 1902.Connection circuitry 1907 is provided for connecting the TAPcontroller's Clock-DR, Capture-DR, and Update-DR to the boundary scanregister's CK, CS and UC inputs respectively during TAP controlledoperation, or for connecting the boundary scan register's CK, CS, and UCinputs to TCK, TMS/CS, and a STP update control (STPUC) signalrespectively during STP controlled operation. The STPUC signal will bedescribed in more detail in regard to FIGS. 20A-C. An example CKmultiplexer 1922 is shown in FIG. 19C, an example UC multiplexer 1924 isshown in FIG. 19D, and an example CS multiplexer 1926 is shown in FIG.19E. All multiplexers reside in connection circuit 1907 and all receiveboundary scan register CK, CS, UC selection signals CKSEL, CSSEL, andUPSEL from the TAP instruction register via bus 504.

The process for selecting the boundary scan register between TDI/SI andTDO/SO and switching the TAP/STP interface into the STP controlled modeis similar to that described for selecting the scan circuit 501 of FIGS.5-7. While in the TAP controlled mode, a boundary scan instruction isscanned into and updated from the instruction register. The outputs fromthe instruction register are input to the TAP lock circuit 508,connection circuit 1907, and OR gate 1903, via bus 504. In response tothe signals from bus 504, the TAP lock circuit outputs a low on Lock Outwhich disables the TAP and enables SO output buffer 1902 via OR gate1903. The Lock Out signal is allowed to pass through OR gate 1903 sincea boundary scan register SO enable signal to OR gate 1903 from theinstruction register is set low. Also, in response to the signals frombus 504, connection circuitry 1907 connects TMS/CS to the boundary scanregister's CS input, the TCK to boundary scan register's CK input, andthe STPUC signal to the boundary scan register's UC input. Again, itshould be noted that the SO buffer 1902, OR gate 1903, and connectioncircuitry 1907 is separate from the SO buffers 506 and 1005, OR gates506 and 1005, and connection circuits 505 and 1004 of FIGS. 5A and 10A.Also the boundary scan instruction control signals to connectioncircuitry 1907, SO buffer 1902, and OR gate 1903 is separate from thescan test instruction and bypass instruction control signals toconnection circuitry 505 and 1004, SO buffers 506 and 1005, and OR gates512 and 1006. When the boundary scan register SO buffer 1902 is enabledto drive out on TDO/SO, all other SO buffers 506 and 1005 are disabledto avoid contention during STP controlled boundary scan testing.

FIG. 20A illustrates an example timing diagram of STP controlled scanoperations to the boundary scan register 1901 of FIG. 19A. During STPcontrolled operations, the boundary scan register CS input is driven byTMS/CS via the multiplexer of FIG. 19E, the CK input is driven by TCKvia the multiplexer of FIG. 19C, and the UC input is driven by STPUC viathe multiplexer of FIG. 19D. Each STP controlled boundary scan operationcycle is defined by; (1) a shifting step where data is shifted throughFF's 1905 from TDI/SI to TDO/SO, (2) an update step where the datashifted into FFs 1905 is updated into FFs 1904, and (3) a capture stepwhere FI data is captured into FFs 1905. In this STP controlled example,shifting of data through the boundary scan register 1901 occurs on therising edge of each CK while CS is high, from a first shift to a lastshift. Following the last shift, the CS transitions low. On the fallingedge of the last shift CK, and while CS is low, the UC is generated toproduce the update step mentioned above. The STPUC signal that drivesthe UC signal is produced in response to the TMS/CS and TCK signals.FIG. 20B illustrates and example circuit for producing the STPUC signalin response to appropriate TMS/CS and TCK signal conditions. The UCsignal clocks FFs 1904 to update the data from FFs 1905 to the FOoutputs of the boundary scan register. On the next rising CK edge afterthe update step, FFs 1905 perform the capture step of loading data fromthe FI inputs of the boundary scan register. These shift, update, andcapture steps are indicated in the timing diagram of FIG. 20A and arerepeated during each STP controlled boundary scan cycle.

In the timing diagram, the capture step occurs one half of a CK periodafter the update step. This allows STP controlled boundary scan testoperations to be more effective at performing delay tests thanconventional TAP controlled boundary scan test operations. This improveddelay testing advantage will be described in more detail in regard toFIGS. 21 and 22.

The STP controlled timing can be used to simultaneously operate both theboundary scan cell 2010, including MUX 2004, FF 2001, FF 2002, and MUX2006, and internal scan cell 2011, including MUX 2012, types of FIG.20C. The advantage of being able to operate both cell types during STPcontrolled testing will be described in more detail in regard to FIG.22.

FIG. 21 illustrates an IC 2100 containing cores 1-3 2106, 2108, 2110,each core containing a TAP/STP interface coupled to tester controlledscan path 910 and a boundary scan register 1901. In this example, thecores have been setup, as described in regard to FIG. 19A, for STPcontrolled boundary scan testing of connection circuits 2101-2104. Core1 interfaces to the external tester 2108 via connection circuitry 2101,Cores 1 and 2 interface internally via connection circuit 2102, Cores 2and 3 interface internally via connection circuit 2103, and Core 3interfaces to the external test connection circuit 2104. Connectioncircuits 2101-2104 are the functional connections between the cores andIC input and output pins to enable the cores to operate and produce theIC's intended functionality. Connection circuits 2101-2104 contain bothsimple connections that pass signals through wires and complexconnections that pass signals through logic circuitry. Both simple andcomplex connection types need to be tested using the STP controlledboundary scan test operation.

The STP controlled boundary scan testing is achieved by the testercontrolling the scan path 910 to repetitively cycle the core TAP/STPinterfaces through the shift, capture, and update steps described inregard to FIG. 20A. The shift step loads stimulus data into the boundaryscan registers (BSR) 1901 from the tester and unloads capture responsedata from the BSRs 1901 to the tester. Following the shift step, theupdate step outputs the loaded stimulus data from the FO outputs of theBSRs. Following the update step, the capture step loads response datainto the BSRs from the FI inputs. During the update and capture stepsequence, test signals pass through connection circuits 2101-2104 totest both the simple and complex connection types. Connection circuits2102 and 2103 are tested by using only the BSRs 1901 of cores 1, 2, and3. Connection circuits 2101 and 2104 are tested using the externaltester and BSRs 1901 of cores 1 and 3.

Two types of STP controlled boundary scan tests may be performed, astructural test which verifies that test signals can propagate throughthe simple and complex connections, and a delay test which verifies thatthe test signals propagate through the simple and complex connectionswithin a given amount of time. The structural test may successfullypropagate the test signals through the connections, but the IC may failto operate at its rated speed due to certain ones of the connectionshaving a slow signal propagation time. Therefore, the delay test isimportant since it allows testing that the test signals can successfullypropagate through the connection within a time frame that enables the ICto operate at it rated speed. A TAP controlled boundary scan test canalso perform the structural and delay tests. A TAP controlled structuraltest is just as effective as the STP controlled structural test.However, as will described below, a TAP controlled delay test is not aseffective as the STP controlled delay test.

From the timing diagram of FIG. 20A it is seen that the STP controlledcapture step occurs on the rising CK edge following the falling CK edgethat initiates the update step. If CK is driven by the tester at a highfrequency, very effective delay testing can be achieved using STPcontrolled boundary scan testing since the delay test occurs within onehalf a CK period. TAP controlled delay testing is not as effective asSTP controlled delay testing do to the state transition mapping of theTAP controller state machine of FIG. 2. For example, the steps ofupdating data in the Update-DR state then capturing data in theCapture-DR state are separated in time by two and one half CK periods(CK is TCK). This can be seen by the rising CK edge activated statetransitions from Update-DR to Select-DR to Capture-DR to Shift-DR, andby recognizing that data is updated on the falling edge of CK during theUpdate-DR state and captured on the rising edge of CK during theCapture-DR to Shift-DR state transition. Thus a TAP controlled delaytest operates using two and a half CK periods, as opposed to the onehalf CK period used in the STP controlled delay test.

FIG. 22 illustrates an IC or core 2200 being tested via the TAP/STPinterface. In this example, the boundary scan registers (BSR) 2201-2202and internal scan registers (ISR) 2203-2204 of the IC or core have beenserially daisy-chained together between TDI/SI and TDO/SO and placed inan STP controlled test mode using a BSR&ISR scan instruction designedfor that purpose. Substituting the daisy-chained BSR and ISR scanregister of FIG. 22 for the boundary scan register 1901 of FIG. 19A, itshould be clear from the previous instruction control descriptions howthe BSR&ISR scan instruction may be loaded into the TAP's instructionregister to configure the TAP/STP interface into the configuration shownin FIG. 22.

During test, a tester coupled to the TAP/STP interface repetitivelyexecutes STP controlled scan cycles on the FIG. 22 daisy-chained BSR&ISRscan register to test the combinational logic circuits 2205-2207residing between the BSR 2201-2202 and ISR 2203-2204 scan registersections. Each scan cycle includes the shift, update, and capture stepsdescribed in the timing diagram of FIG. 20A. Conventional boundary scancells 2010 of FIG. 20C are used in the BSR and conventional internalscan cells 2011 of FIG. 20C are used in the ISR. During the shift step,scan cells 2010 and 2011 shift data from SI to SO through thedaisy-chained BSR& ISR register from TDI/SI to TDO/SO. During the shiftstep, the FO outputs of scan cells 2010 do not ripple with the SO outputbecause the update FF 2002 maintains the FO output at a constant stateduring the shift step. However, the FO output of scan cells 2011 doripple with the SO output. During the update step, the FO output of thescan cells 2010 change as the update FF 2002 is loaded by the UC controlsignal of FIG. 20A. Prior to the update step, the FO outputs of the scancells 2011 have already been established by the last shift operation ofFIG. 20A. So, from the STP controlled timing diagram of FIG. 20A, it isseen that the FO outputs of the ISR scan cells 2011 are made availableimmediately after the last shift operation, whereas the availability ofthe FO outputs of the BSR scan cells 2010 are delayed until the updatestep, which is one half CK period after the last shift operation. Duringthe capture step, the data on the FI inputs of BSR scan cells 2010 andISR scan cell 2011 are loaded into shift FF 2001 and 2003 respectively.

The STP controlled scan test example of FIG. 22 provides a method ofallowing both conventional boundary scan cells 2010 and conventionalinternal scan cells 2011 to be daisy-chained together and operated usingthe common shift, update, and capture steps shown in the timing diagramof FIG. 20A. Traditionally, it has been necessary to access the BSRs2201-2202 separately using the TAP controller of FIG. 1A. Alsotraditionally, it has been necessary to access the ISRs 2202-2203separately using the STP controlled CS and CK signal sequencing of FIG.20A. The reason for this is because the boundary scan cells 2010 of theBSR require the update step (i.e. Update-DR state of FIG. 2) between theshift (Shift-DR state of FIG. 2) and capture (Capture-Dr state of FIG.2) steps to load data into the update FF 2002. Since internal scan cells2011 do not have an update FF to load, they only require the shift andcapture steps provided by the CS and CK signals of the STP timingdiagram of FIG. 20A. Thus the difficulty of daisy-chaining BSRs2201-2202 and ISRs 2203-2204 together as shown in FIG. 22 and operatingthe daisy-chained BSR&ISR scan register using either TAP control or STPcontrol has been how to resolve the update step situation. Some knownmethods for handling the update step in internal scan cells 2011 whenusing the TAP controller include; (1) gating off the CK input to theinternal scan cells 2011 during the update (Update-DR state) step, or(2) using a three input multiplexer in place of the two inputmultiplexer in internal scan cells 2011 and controlling the thirdmultiplexer input to feed the output of the shift FF 2003 to the inputof shift FF 2003 during the update step (Update-DR state), such that thestate of the shift FF is maintained during the update step. The drawbackof the first method is that it requires inserting gating circuitry inthe CK tree wiring, which should be avoided since clock tree routing iscritical in an IC or core. The drawback of the second method is that itadds circuitry (three input multiplexer vs two input multiplexer) toeach internal scan cell 2011, which should be avoided because itincreases test circuit overhead in the IC or core.

To overcome these conventional drawbacks of accessing scan registerswhich include mixtures of daisy-chained BSR 2201-2202 and ISR 2203-2204sections, the present invention provides and appropriately controls theUC signal of FIG. 20A to perform the update step required for the BSRsections of daisy-chained BSR& ISR scan registers. In FIG. 20A, the CSand CK signal timing for performing the shift and capture steps ininternal scan cells 2011 is conventional. However, the generation andpositioning of the UC signal between the last shift step and the capturestep is new and is what allows the present invention to easily operatescan registers which include daisy-chained BSR and ISR sections withoutincurring the previously mentioned drawbacks. The use of the UC signalis transparent to internal scan cells 2011 since they only haveconnections to CS and CK. Also, the timing of the UC signal occurs suchthat it does not effect the conventional timing of the CS and CK signalsto the internal scan cells 2011. The timing diagram of FIG. 20A not onlytransparently provides the BSR required update step, via UC, it does soin a way that supports effective delay testing of combinational logiccircuits 2205 and 2207 that reside between BSR and ISR sections of thedaisy-chained scan register of FIG. 22. This can be seen in FIG. 20A,where the BSR sections of the FIG. 22 scan register respond to the UCsignal to update their FO outputs one half a CK period prior to thecapture step that causes the scan cells 2010 and 2011 of the BSR and ISRscan register sections to load data at their FI inputs. For the samereasons stated for the boundary scan delay test of FIG. 21, the STPcontrolled delay test of the combinational logic circuits 2205-2207 ofFIG. 22 is more effective than a TAP controlled delay test of the samecircuits 2205-2207.

FIGS. 9, 11, 13, 15, 17, 18, and 21 of the present invention haveillustrated the TAP/STP interfaces as always being connected to the scanpath 910. While this is one way to connect TAP/STP interfaces, thefollowing description will describe another method of providing accessto TAP/STP interfaces. The following connection approach was developedto provide selective access to one or more TAP domains existing within asystem IC. The word domain simply indicates the circuitry the TAPprovides access to, such as the circuits of FIGS. 1C-1F. In thedescription below, an overview of the TAP domain access approach will begiven, then improvements to the TAP domain access approach will bedescribed to show how it can be used to provide selective access to oneor more TAP/STP domains as well. The TAP domain selection approach isthe subject of related provisional patent application Ser. No.60/207,691 filed May 26, 2000, entitled “Improvements In or Related to1149.1 TAP Linking Modules”, which is incorporated herein by reference.

Overview of TAP Domain Access

IEEE 1149.1 TAPs may be utilized at both IC and intellectual propertycore design levels. TAPs serve as serial communication ports foraccessing a variety of embedded circuitry within ICs and coresincluding; IEEE 1149.1 boundary scan circuitry, built in test circuitry,internal scan circuitry, IEEE 1149.4 mixed signal test circuitry, IEEEP5001 in-circuit emulation circuitry, and IEEE P1532 in-systemprogramming circuitry. Selectable access to TAPs within ICs is desirablesince in many instances being able to access only the desired TAP(s)leads to improvements in the way testing, emulation, and programming maybe performed within an IC. The following describes how TAP domainsembedded within an IC may be selectively accessed using 1149.1instruction scan operations.

FIG. 23 illustrates an example arrangement for connecting multiple TAPdomains within an IC 2300 to a single scan path. Each TAP domain in FIG.23 is a complete TAP architecture like that shown and described inregard to FIG. 1A. While only one IC TAP domain 2301 exists in an IC,any number of core TAP domains 1-N 2302-2303 may exist within an IC. Asseen in FIG. 23, the IC TAP domain and Core 1-N TAP domains aredaisy-chained between the IC's TDI and TDO pins. All TAP domains areconnected to the IC's TMS, TCK, and TRST signals and operate accordingto the state diagram of FIG. 2. During instruction scan operations,instructions are shifted into each TAP domain instruction register. Onedrawback of the TAP domain arrangement of FIG. 3 is that it does notcomply with the IEEE 1149.1 standard, since, according to the rules ofthat standard, only the ICs TAP domain 2301 should be present betweenTDI and TDO when the IC is initially powered up. A second drawback ofthe TAP domain arrangement of FIG. 23 is that it may lead tounnecessarily complex access for testing, in-circuit emulation, and/orin-circuit programming functions associated with ones of the individualTAP domains.

For example, if scan testing is required on circuitry associated withthe Core 1 TAP domain, each of the scan frames of the test pattern setdeveloped for testing the Core 1 circuitry must be modified from theiroriginal form. The modification involves adding leading and trailing bitfields to each scan frame such that the instruction and data registersof the leading and trailing TAP domains become an integral part of thetest pattern set of Core 1. Serial patterns developed for in-circuitemulation and/or in-circuit programming of circuitry associated with theTAP domain of Core 1 must be similarly modified. To overcome these andother drawbacks of the TAP arrangement of FIG. 23, the TAP selectionarchitecture described below is provided.

FIG. 24 illustrates the preferred structure for connecting multiple TAPdomains within an IC according to U.S. Pat. No. 7,058,862, issued Jun.6, 2006. The structure includes input and output linking circuitry 2401and 2402 for connecting one or more TAP domains 2410, 2412, 2414 to theICs TDI, TDO, TMS, TCK and TRST pins, and a TAP Linking Module (TLM)circuit 2403 for providing the control to operate the input and outputlinking circuitry.

The input linking circuitry receives as input; (1) the TDI, TMS, TCK,and TRST IC pins signals, (2) the TDO outputs from the IC TAP (ICT)domain (TDO_(ICT)), the Core I TAP (CIT) domain (TDO_(CIT)), and theCore N TAP (CNT) domain (TDO_(CNT)), and (3) TAP link control bus 2404input from the TLM. The TCK and TRST inputs pass unopposed through theinput linking circuitry to be input to each TAP domain. The TMS input tothe input linking circuitry is gated within the input linking circuitrysuch that each TAP domain receives a uniquely gated TMS output signal.As seen in FIG. 24, the IC TAP domain receives a gated TMS_(ICT) signal,the Core 1 TAP domain receives a gated TMS_(CIT) signal, and the Core NTAP domain receives a gated TMS_(CNT) signal. Example circuitry forproviding the gated TMS_(ICT), TMS_(CIT), and TMS_(CNT) signals is shownin FIG. 25. In FIG. 25, the ENA_(ICT), ENA_(CIT), and ENA_(CNT) signalsused to gate the TMS_(ICT), TMS_(CIT), and TMS_(CNT) signals,respectively, come from the TLM via the TAP link control bus.

From FIG. 25 it is seen that TMS_(CNT) can be connected to TMS to enablethe Core N TAP domain or be gated low to disable the Core N TAP domain,TMS_(CIT) can be connected to TMS to enable the Core 1 TAP domain or begated low to disable the Core 1 TAP domain, and TMS_(ICT) can beconnected to TMS to enable the IC TAP domain or be gated low to disablethe IC TAP domain. When a TAP domain TMS input (TMS_(CNT), TMS_(CIT),TMS_(ICT)) is gated low, the TAP domain is disabled by forcing it toenter the Run Test/Idle state of FIG. 2. A disabled TAP domain willremain in the Run Test/Idle state until it is again enabled by couplingit to the IC's TMS pin input as mentioned above.

The TDI, TDO_(CNT), TDO_(CIT), and TDO_(ICT) inputs to the input linkingcircuitry are multiplexed by circuitry within the input linkingcircuitry such that each TAP domain receives a uniquely selected TDIinput signal. As seen in FIG. 24, the IC TAP domain receives a TDI_(ICT)input signal, the Core 1 TAP domain receives a TDI_(CIT) input signal,and the Core N TAP domain receives a TDI_(CNT) input signal. Examplecircuitry for providing the TDI_(ICT), TDI_(CIT), and TDI_(CNT) inputsignals is shown in FIG. 26. In FIG. 26, the SELTDI_(ICT), SELTDI_(CIT),and SELTDI_(CNT) control signals used to select the source of theTDI_(ICT), TDI_(CIT), and TDI_(CNT) input signals, respectively, comefrom the TLM via the TAP link control bus. From FIG. 26 it is seen thatTDI_(CNT) can be selectively connected to TDI, TDO_(CIT), or TDO_(ICT),TDI_(CIT) can be selectively connected to TDI, TDO_(CNT), or TDO_(ICT),and TDI_(ICT) can be selectively connected to TDI, TDO_(CNT), orTDO_(CIT).

The output linking circuitry receives as input; (1) the TDO.sub.CNToutput from the Core N TAP domain, the TDO.sub.CIT output from the Core1 TAP domain, the TDO.sub.ICT output from the IC TAP domain, and TAPlink control bus 2404 input from the TLM. As seen in FIG. 24, the outputlinking circuitry outputs a selected one of the TDO.sub.CNT,TDO.sub.CIT, and TDO.sub.ICT input signals to the TLM via the outputlinking circuitry TDO output. Example circuitry MUX 2702 for providingthe multiplexing of the TDO.sub.ICT, TDO.sub.CIT, and TDO.sub.CNTsignals to the TDO output is shown in FIG. 27. In FIG. 27, theSEL.sub.TDO control input used to switch the TDO.sub.ICT, TDO.sub.CIT,or TDO.sub.CNT signals to TDO come from the TLM via the TAP link controlbus. From FIG. 27 it is seen that any one of the TDO.sub.CNT,TDO.sub.CIT, and TDO.sub.ICT signals can be selected as the input sourceto the TLM.

The TLM circuit receives as input the TDO output from the output linkingcircuitry and the TMS, TCK, and TRST IC input pin signals. The TLMcircuit outputs to the IC's TDO output pin. From inspection, it is seenthat the TLM lies in series with the one or more TAP domains selected bythe input and output linking circuitry.

As described above, the TLM's TAP link control bus 2404 is used tocontrol the input and output connection circuitry to form desiredconnections to one or more TAP domains so that the one of more TAPdomains may be accessed via the IC's TDI, TDO, TMS, TCK, and TRST pins.The TAP link control bus signals are output from the TLM during theUpdate-IR state of the TAP controller state diagram of FIG. 2.

FIG. 28A illustrates in detail the structure of the TLM 2403. The TLMconsists of a TAP controller 2801, instruction register 2802,multiplexer 2803, and 3-state TDO output buffer 2804. The TAP controlleris connected to the TMS, TCK and TRST signals. The TDI input isconnected to the serial input (I) of the instruction register and to afirst input of the multiplexer. The serial output (O) of the instructionregister is connected to the second input of the multiplexer. Theparallel output of the instruction register is connected to the TAP linkcontrol bus 2404 of FIG. 24. The output of the multiplexer is connectedto the input of the 3-state buffer 2804. The output of the 3-statebuffer is connected to the IC TDO output pin. The TAP controller outputscontrol (C) to the instruction register, multiplexer, and 3-state TDOoutput buffer via bus 2805. The TAP controller responds to TMS and TCKinput as previously described in regard to FIGS. 1A and 2. Duringinstruction scan operations, the TAP controller enables the 3-state TDObuffer and shifts data through the instruction register from TDI to TDO.During data scan operations, the TAP controller enables the 3-state TDObuffer and forms a connection, via multiplexer 2803, between TDI andTDO.

FIG. 28B illustrates the instruction register 2802 in more detail. Theinstruction register consists of a shift register 2820, TAP link decodelogic 2822, and update register 2824. The shift register has the serialinput (I), serial output (O), control (C) inputs shown in FIG. 28A,parallel outputs to the TAP link decode logic, and parallel inputs forloading fixed logic 0 and 1 settings. The fixed logic 0 and 1 inputs areprovided for capturing logic 0 and 1 data bits into the first twoinstruction shift register bit positions closest to TDO, which is arequirement for IEEE 1149.1 compliant instruction shift registers. Theparallel output from the instruction register is input to TAP linkdecode logic. The parallel output from the TAP link decode logic isinput to the update register. The parallel output of the update registeris connected to the TAP link control bus 2402 to provide control inputto the input and output linking circuitry 2401 and 2402 of FIG. 24.During the Capture-IR state of FIG. 2, the shift register captures data(0 & 1) on the parallel input. During the Shift-IR state of FIG. 2, theshift register shifts data from TDI (I) to TDO (O). During the Update-IRstate of FIG. 2, the update register loads the decoded instructioncontrol input from the TAP link decode logic and outputs the decodedinstruction control onto the TAP link control bus 2404.

FIG. 29 illustrates various possible arrangements 2901-2907 of TAPdomain connections during 1149.1 instruction scan operations. Sinceduring instruction scan operations, the TLM's instruction register isphysically present and in series with the connected TAP domain(s)instruction register(s), the instruction scan frame for each arrangementwill be augmented to include the TLM's instruction register bits. It isassumed at this point that the TLM's instruction shift register of FIG.28 is 3 bits long and that the 3 bit instructions have been decoded bythe TLM's instruction register to uniquely select a different TAP domainconnection arrangement between the ICs TDI and TDO pins. For example andas indicated in FIG. 29, shifting in the following 3 bit TLMinstructions and updating them from the TLM to be input to the input andoutput linking circuitry will cause the following TAP domain connectionsto be formed.

As seen in arrangement 2901, a “000” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP domainto be enabled and connected in series with the TLM between the TDI andTDO IC pins.

As seen in arrangement 2902, a “001” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP domainand the Core 1 TAP Domain to be enabled and connected in series with theTLM between the TDI and TDO IC pins.

As seen in arrangement 2903, a “010” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP domainand the Core N TAP Domain to be enabled and connected in series with theTLM between the TDI and TDO IC pins.

As seen in arrangement 2904, a “011” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP domain,the Core 1 TAP Domain, and the Core N TAP domain to be enabled andconnected in series with the TLM between the TDI and TDO IC pins.

As seen in arrangement 2905, a “100” instruction shifted into andupdated from the TLM instruction register will cause the Core I TAPDomain to be enabled and connected in series with the TLM between theTDI and TDO IC pins.

As seen in arrangement 2906, a “101” instruction shifted into andupdated from the TLM instruction register will cause the Core 1 TAPDomain and Core N TAP domain to be enabled and connected in series withthe TLM between the TDI and TDO IC pins.

As seen in arrangement 2907, a “110” instruction shifted into andupdated from the TLM instruction register will cause the Core N TAPDomain to be enabled and connected in series with the TLM between theTDI and TDO IC pins.

At power up of the IC, the TLM 3-bit instruction shall be initialized to“000” to allow only the IC TAP domain arrangement 2901 to be enabled andcoupled between TDI and TDO. This complies with the IC power uprequirement established in the IEEE 1149.1 standard. Following power up,an instruction scan operation can be performed to shift instruction datathrough the IC TAP domain and the serially connected TLM to load a newIC TAP domain instruction and to load a new 3 bit instruction into theTLM. If the power up IC TAP domain arrangement 2901 is to remain ineffect between TDI and TDO, the 3 bit “000”=0 TLM instruction of FIG. 29will be re-loaded into the TLM instruction register during the abovementioned instruction scan operation. However, if a new TAP domainarrangement is to desired between TDI and TDO, a different 3 bit TLMinstruction will be loaded into the TLM instruction register during theabove mentioned instruction register scan operation.

From the description given above, it is clear that a different TAPdomain arrangement may be selected by the TLM's instruction registerfollowing each 1149.1 instruction scan operation, more specificallyduring the Update-IR state (FIG. 2) of each instruction scan operation.Thus the TAP domain selection process comprises only the single step ofperforming an instruction scan operation to load instructions into theinstruction registers of the currently selected TAP domains and TLM.

The following briefly re-visits and summarizes the operation of the TLMand input and output linking circuitry to clarify the TAP domainarrangement switching illustrated in FIG. 29. As previously described inregard to FIG. 24, the TMS inputs of enabled TAP domains are coupled tothe IC's TMS input pin (via the gating circuitry of FIG. 25), while theTMS inputs of disabled TAP domains are gated to a logic low (via thegating circuitry of FIG. 25). Also, enabled TAP domains are seriallyconnected (via the multiplexers of FIGS. 26 and 27) to form the desiredserial TAP domain connection between the IC's TDI and TDO pins, theconnection including the TLM. All the control for enabling or disablingthe TAP domain TMS inputs and for forming serial TAP domain connectionsbetween the IC's TDI and TDO pins comes from the TLM's TAP link controlbus. The control output from the TAP link control bus changes stateduring the Update-IR state of the TAP state diagram of FIG. 2. So, allTAP domain connection arrangement changes take place during theUpdate-IR state.

FIG. 30 is provided to illustrate that during 1149.1 data scanoperations the TLM 2403 is configured, as described in regard to FIG.28, to simply form a connection path between the output of the selectedTAP domain arrangement 3001-3007 and the IC's TDO pin. Thus the TLM 2403does not add bits to 1149.1 data scan operations as it does for 1149.1instruction scan operations. TAP domain arrangements 3001-3007 for1149.1 data scans are the same as TAP domain arrangements 2901-2907 for1149.1 instruction scans, with the exception that during data scans theoutput of the selected TAP domain arrangement 3001-3007 passes directlythrough the TLM to TDO, as opposed to passing through the TLM'sinstruction register during instruction scans to TAP domain arrangements2901-2907.

FIG. 31 illustrates how the structure of the TLM architecture of FIG. 24may be adapted to support TAP/STP domains 3110, 3112, 3114 instead ofTAP domains. From FIG. 31 it is seen that the basic structure of the TLMarchitecture of FIG. 24 is maintained when using TAP/STP domains inplace of TAP domains. The changes seen in FIG. 31 involve renaming TDIto TDI/SI, TDO to TDO/SO, TMS to TMS/CS, TDI.sub.CNT to TDI/SI.sub.CNT,TDI.sub.CIT to TDI/SI.sub.CIT, TDI.sub.ICT to TDI/SI.sub.ICT,TMS.sub.CNT to TMS/CS.sub.CNT, TMS.sub.CIT to TMS/CS.sub.CIT,TMS.sub.ICT to TMS/CS.sub.ICT, TDO.sub.CNT to TDO/SO.sub.CNT,TDO.sub.CIT to TDO/SO.sub.CIT, and TDO.sub.ICT to TDO/SO.sub.ICT, torepresent the different signal types used by the TAP/STP domains. Thename of the TAP link control bus of FIG. 24 has also been changed toTAP/STP link control bus 3104 in FIG. 31.

FIGS. 32 and 33 represent the TAP/STP domain signal name substitutionfor the TAP domain signal names in the TMS gating circuitry and TDImultiplexing circuitry 3302, 3304, 3306 of the input circuitry 3101 ofFIG. 31. The control inputs to the TDI/SI multiplexer circuitry of FIG.33, from the TAP/STP link control bus of FIG. 31, are also changed fromSELTDI.sub.CNT to SELTDI/SI.sub.CNT, SELTDI.sub.CIT toSELTDI/SI.sub.CIT, and SELTDI.sub.ICT to SELTDI/SI.sub.ICT. FIG. 34, MUX3402, represents the TAP/STP domain signal name substitution for the TAPdomain signal names of the output circuitry 3102 of FIG. 31. The gatingand multiplexing circuitry of FIGS. 32-34 respond to TLM 3103instruction control output on TAP/STP control bus 3104 as previouslymentioned. The only circuit changes between the TLM architecture ofFIGS. 24 and 31, excluding the substitution of TAP/STP domains for TAPdomains and the signal renaming mentioned above lies within TLM 3103 asdescribe below.

It should be clear that the TMS/CS_(CNT), TMS/CS_(CIT), TMS/CS_(ICT)outputs of the AND gates in FIG. 32 are each input to a respective ANDgate 503 (FIG. 7) of the Core N, Core 1, and IC TAP/STP interfaces ofFIG. 31. From this, it should clear that a three input AND gate 503(FIG. 7) could be substituted for the two input AND gate 503 to allowthe third input to directly input the ENA_(CNT), ENA_(CIT), andENA_(ICT) signals from the TLM 3103. This would eliminate the need forthe AND gates of FIG. 32 and reduce the signal propagation delay of theTMS/CS input to the TAP controller of the TAP/STP interfaces.

FIG. 35A illustrates a detail view of TLM 3103 of FIG. 31. Like TLM 2403of FIG. 28, TLM 3103 contains a TAP controller 3501, instructionregister 3502, multiplexer 3503, and 3-state buffer 3504. Unlike TLM2403, TLM 3103 additionally contains logic gates 3505, 3506, 3507, and aTAP lock circuit 3508. The TAP controller outputs the Update-IR signal3509 to TAP lock circuit 3508, as described in regard to FIG. 7. Theinstruction register 3502 outputs the Lock in signal 3510 to the TAPlock circuit, as described in FIG. 7. The TAP lock circuit outputs theLock out signal 3511 from the TLM and to gates 3505, 3506, and 3507.Gate 3507 serves the same function as gate 503 of FIG. 7, that beinggating the TMS input to the TAP controller 3501 on when Lock out is highand off when Lock out is low. When Lock out is high (TAP unlocked),gates 3505 and 3506 pass signals from the TAP controller bus 3512 tooperate multiplexer 3503 and 3-state buffer 3504, during TAP controllerinstruction and data scan operations as previously described with TLM2403 of FIG. 28. When Lock out is low (TAP is Locked), the output ofgate 3505 is set, via the Lock out signal, to select the TDI/SI input tomultiplexer 3503 to be input to buffer 3504. Also while Lock out is low,the output of gate 3506 is set, via the Lock out signal, to enable theoutput of buffer 3504 to drive TDO/SO.

The TAP lock process of, (1) inputting an instruction into theinstruction register of TLM 3103 to set the Lock in signal 3510 high,(2) clocking the Lock in signal into the TAP lock circuit 3508 to setthe Lock out signal 3511 low, and (3) disabling the TAP controller 3501and enabling the TAP Lock circuit 3508 in response to the Lock outsignal going low, is the same as described previously in regard to FIGS.7, 8A and 8B. While the TAP controller 3501 is locked and the TAP Lockcircuit 3508 is enabled, STP control of TMS/CS can occur as described inregard to FIGS. 7, 8A, and 8B without unlocking the TAP controller 3501and without disabling the TAP Lock circuit 3508. The process ofunlocking the TAP controller 3501 and disabling the TAP Lock circuit3508 by setting the TMS/CS input to the TAP Lock circuit 3508 low for arequired number of TCK inputs is also the same as previously describedin regard to the TAP lock circuit descriptions of FIGS. 8A and 8B.

FIG. 35B illustrates in detail the changes required to instructionregister 3502 to enable TLM 3103 to operate in a first mode to selectand access TAP/STP domains using TAP control, or operate in a secondmode to select and access TAP/STP domains using STP control. Instructionregister 3502 is similar in structure and operation to instructionregister 2802 in that it has a shift register 3520, a TAP/STP linkdecode logic 3522, and an update register 3524. The differences betweeninstruction registers 3502 and 2802 include; (1) the shift register of3502 is 4 bits long instead of 3 bits in 2802, (2) the TAP/STP linkdecode logic of 3502 is designed to decode the 4 bit instruction insteadof the 3 bit instruction of 2802, and (3) the update register of 3502includes, in addition to the TAP/STP link control bus 3104, an outputfor the Lock in signal 3510.

FIG. 36 illustrates various possible arrangements 3601-3607 of TAP/STPdomain connections during 1149.1 TAP instruction scan operations usingthe TAP/STP architecture of FIG. 31. Since during instruction scanoperations, the TLM's 3103 instruction register is physically presentand in series with the connected TAP/STP domain(s) instructionregister(s), the instruction scan frame for each arrangement will beaugmented to include the TLM's 3103 4 instruction register bits. Aspreviously mentioned, the TLM's 3103 instruction shift register of FIG.35B is 4 bits long and the 4 bit instructions have been decoded by theTLM's 3103 instruction register to uniquely select a different TAP/STPdomain connection arrangement between the ICs TDI/SI and TDO/SO pins.For example and as indicated in FIG. 36, shifting in the following 4 bitTLM instructions and updating them from TLM 3103 to the input and outputlinking circuitry 3101 and 3102 will cause the following TAP/STP domainconnections to be formed.

As seen in arrangement 3601, a “0000” instruction shifted into andupdated from the TLM instruction register will cause the IC TAP/STPdomain to be enabled and connected in series with the TLM between theTDI/SI and TDO/SO IC pins.

As seen in arrangement 3602, a “0001” instruction shifted into andupdated from the TLM instruction register will cause the IC and Core 1TAP/STP domains to be enabled and connected in series with the TLMbetween the TDI/SI and TDO/SO IC pins.

As seen in arrangement 3603, a “0010” instruction shifted into andupdated from the TLM instruction register will cause the IC and Core NTAP/STP domains to be enabled and connected in series with the TLMbetween the TDI/SI and TDO/SO IC pins.

As seen in arrangement 3604, a “0011” instruction shifted into andupdated from the TLM instruction register will cause the IC, Core 1, andCore N TAP/STP domains to be enabled and connected in series with theTLM between the TDI/SI and TDO/SO IC pins.

As seen in arrangement 3605, a “0100” instruction shifted into andupdated from the TLM instruction register will cause the Core 1 TAP/STPdomain to be enabled and connected in series with the TLM between theTDI/SI and TDO/SO IC pins.

As seen in arrangement 3606, a “0101” instruction shifted into andupdated from the TLM instruction register will cause the Core 1 and CoreN TAP/STP domains to be enabled and connected in series with the TLMbetween the TDI/SI and TDO/SO IC pins.

As seen in arrangement 3607, a “0110,” instruction shifted into andupdated from the TLM instruction register will cause the Core N TAP/STPdomain to be enabled and connected in series with the TLM between theTDI/SI and TDO/SO IC pins.

At power up of the IC, the TLM 3103 4-bit instruction is initialized to“0000” to allow only the IC TAP/STP domain arrangement 3601 to beenabled and coupled between TDI/SI and TDO/SO, to comply with the IEEE1149.1 standard. Following power up, an instruction scan operation canbe performed to shift instruction data through the IC TAP domain and theserially connected TLM 3103 to load a new IC TAP/STP domain instructionand to load a new 4 bit instruction into the TLM.

From the description given above, it is clear that a different TAP/STPdomain arrangement may be selected by the TLM 3103 instruction registerfollowing each 1149.1 instruction scan operation, more specificallyduring the Update-IR state (FIG. 2) of each instruction scan operation.Thus the TAP/STP domain selection process comprises only the single stepof performing an instruction scan operation to load instructions intothe instruction registers of the currently selected TAP/STP domains andTLM 3103.

FIG. 37 is provided to illustrate that during 1149.1 data scanoperations the TLM 3103 is configured, as described in regard to FIG.35A, to simply form a connection path between the output of the selectedTAP/STP domain arrangement 3701-3707 and the IC's TDO/SO pin. Thus theTLM 3103 does not add bits to 1149.1 data scan operations as it does for1149.1 instruction scan operations. TAP/STP domain arrangements3701-3707 for 1149.1 data scans are the same as TAP/STP domainarrangements 3601-3607 for 1149.1 instruction scans, with the exceptionthat during data scans the output of the selected TAP/STP domainarrangement 3701-3707 passes directly through the TLM to TDO/SO, asopposed to passing through the TLM's instruction register duringinstruction scans to TAP/STP domain arrangements 3001-3007.

Comparing the operation of the TAP controlled instruction and data scanoperations of FIGS. 36 and 37 to the TAP controlled instruction and datascan operations of FIGS. 29 and 30, it is clear that the TLMarchitectures of FIG. 31 (using TAP/STP domains) and FIG. 24 (using TAPdomains) are similar. This is because in both TLM architectures of FIGS.31 and 24, the selected TAP or TAP/STP domains are receptive to beingaccessed using IEEE 1149.1 TAP controlled instruction (FIGS. 36 and 29)and data (FIGS. 37 and 30) scan operations.

The process of selecting a TAP/STP domain arrangement of FIG. 31,placing the selected TAP/STP domain arrangement in the STP controlledmode, and accessing the selected TAP/STP domain arrangement using STPcontrol is as follows. This process example will start in TAP/STP domainarrangement 3601 of FIG. 36, then switch to TAP/STP domain arrangement3604 of FIG. 36, then switch the TAP/STP interfaces of the TAP/STPdomain arrangement 3604 from TAP control to STP control.

A first TAP controlled instruction scan is performed on TAP/STP domainarrangement 3601 to load instructions into the IC TAP/STP domain and theTLM 3103. The instruction loaded into the TLM is “0011” and theinstruction loaded into the IC TAP/STP is say an IEEE 1149.1 standardbypass instruction, a well known 1149.1 instruction. In response to the“0011” TLM instruction, the TLM architecture of FIG. 31 switches fromselecting the TAP/STP domain arrangement 3601 between TDI/SI and TDO/SOto selecting TAP/STP domain arrangement 3604 between TDI/SI and TDO/SO,as previously described. A second TAP controlled instruction scan isperformed through the IC, Core 1, and Core N TAP/STP domains and TLM ofarrangement 3604. This second instruction scan loads an STP controlledtest instruction, like the previously described STP controlled scan testinstruction of FIG. 5-9, into the IC, Core 1, and Core N TAP/STPinterfaces and also loads the TLM with a “1011” instruction which willbring about the STP controlled TAP/STP domain arrangement 3804 seen inFIG. 38. In response to the second instruction scan, the IC, Core 1, andCore N TAP/STP interfaces switch from TAP control to STP control forperforming the STP controlled the scan test instructions, as describedin regard to the daisy-chained cores 1-N of FIG. 9. Also in response tothe second instruction scan, the “1011” instruction loaded into the TLM3103 instruction register causes the TLM to switched from TAP control toSTP control.

The switching of the TLM 3103 from TAP to STP control can best beunderstood by inspection of FIGS. 35A and 35B. When the “1011”instruction is updated from the TLM instruction register, the Lock inoutput 3510 from the TLM instruction register goes high. The high onLock in 3510 is input to TAP lock circuit 3508. In response to the highon Lock in 3510 and when the TAP lock circuit 3508 receives theUpdate-IR clock 3509 from TAP controller 3501, the TAP lock circuit isenabled and drives its Lock out signal 3511 low. The low on Lock out3511 disables TAP controller 3501, forms a connection from TDI/SIthrough multiplexer 3503 to the input of 3-state buffer 3504, andenables the output of 3-state buffer 3504 to drive out on TDO/SO, aspreviously described using gates 3505-3507. Once placed in the STPcontrolled mode, TLM 3103 will remain in the STP controlled mode untilthe previously described TMS/CS escape sequence is input to the TAP lockcircuit's unlock state machine as described in regard to FIGS. 8A and8B.

While in the STP controlled TAP/STP domain arrangement 3804, scantesting of IC, Core 1 and Core N occurs as described previously inregard to the cores 1-N of FIG. 9. In the TAP/STP domain arrangement3804, as in the TAP domain arrangement 3704, the TLM 3103 does not addbits to the scan patterns shifted through the IC, Core 1 and Core Nduring the STP controlled scan test operations. At the end of the STPcontrolled scan test operation to TAP/STP domain arrangement 3804, theTMS/CS is set low to cause the IC, Core 1, Core 2, and TLM to switchfrom the STP controlled mode to the TAP controlled mode, as previouslydescribed in FIGS. 8A and 8B.

After the TAP/STP domain arrangement 3804 returns to the TAP controlledmode, a TAP controlled instruction scan, as described in regard toTAP/STP domain arrangement 3604 is executed to load differentinstructions into the IC, Core 1, Core N and TLM instruction register.The loaded instructions may select another TAP/STP domain arrangementfor testing using either TAP or STP control. In a first example, and inresponse to the above mentioned TAP controlled instruction scanoperation, if the TLM's instruction register were loaded with a “1110”instruction and Core N were loaded with a different type of STPcontrolled test instruction, the Core N TAP/STP domain arrangement 3807would be selected between TDI/SI and TDO/SO for testing Core N via STPcontrol of the different test instruction. In a second example, and inresponse to the above mentioned TAP controlled instruction scanoperation, if the TLM's instruction register were loaded with a “0100”instruction and Core 1 were loaded with a different type of TAPcontrolled test instruction, the Core 1 TAP/STP domain arrangement 3605would be selected between TDI/SI and TDO/SO for testing Core 1 via TAPcontrol of the different test instruction. In general, any TAP/STPdomain arrangement can be selected by the above mentioned TAPinstruction scan operation to load instructions into a currentlyselected TAP/STP domain arrangement and TLM to select a new TAP/STPdomain arrangement and initiate either TAP or STP controlled testing onthe new TAP/STP domain arrangement.

Instructions not related to testing but rather to other embeddedfunctions, such as the in-circuit emulation or in-circuit programmingexamples of FIGS. 1D and 1E, may be loaded into particular TAP/STPdomain arrangements along with a TLM instruction for selecting theparticular TAP/STP domain arrangement to allow the other embeddedfunctions to be operated from either TAP or STP control. Furthermore,any type of instruction may be loaded into a TAP/STP domain and executedusing TAP or STP control with or without the TLM. For example, a fixedTAP/STP domain arrangement as shown in FIG. 9 could execute test,in-circuit emulation, or in-circuit programming instructions usingeither TAP or STP control.

In FIG. 39, a dotted line connection 3901 is shown formed between TLM3103 and IC, Core 1, and Core N TAP/STP domains 3902, 3903, 3904. Thisis provided to illustrate another example implementation of the presentinvention whereby the externally available Lock out signal 3511 of theTLM's TAP lock circuit 3508 is used to provide the Lock Out signal tothe TAP/STP domains which, in this example, do not themselves have TAPlock circuits. In this example, the TAP/STP domain interfaces areequipped with input terminals 3902-3904 for inputting the Lock Outsignal 3511 from TLM 3103 via connection 3901. The TAP/STP domaininterfaces of FIG. 39 utilize the FIG. 6 TAP/STP interface style whichdoes not include the TAP lock circuit, but rather inputs the Lock Outsignal via an input terminal. The operation of this alternaterealization of the present invention to switch between TAP and STPcontrolled modes is the same as previously described. The use of theTLM's TAP lock circuit 3508 to generate the Lock out signal to aplurality of TAP/STP domain interfaces which themselves don't have TAPlock circuits, as shown in FIG. 39, should be understood to be analternate method of implementing the present invention in all TLMexamples described herein. In some implementations, the use of the TLM'sTAP lock circuit 3508 to generate the Lock out signal to other TAP/STPdomain interfaces as shown in FIG. 39 may be preferred since iteliminates the need for each TAP/STP domain interface to have its ownTAP lock circuit.

FIG. 40 illustrates another advantage of the TLM architecture. Today,many legacy, or pre-existing, cores exist that use the conventional TAPinterface of FIG. 1A. These cores do not comprehend or anticipate use ofSTP control as an alternate method of using the TAP interface to accessembedded functions such as boundary scan, internal scan, in-circuitemulation/debug, or in-circuit programming. In FIG. 40, an IC TAP/STPdomain 3904, Core 1 TAP domain 4001, and Core N TAP/STP domain 3902 areshown within the TLM architecture of FIG. 31. The IC TAP/STP, Core 1TAP, and Core N TAP/STP domains are all accessible during TAP controlledoperations. For example, in FIG. 41 all combinations of TAP/STP and TAPdomains arrangements 4101-4107 are shown being accessible between TDI/SIand TDO/SO during TAP controlled instruction scan operations, aspreviously described in regard to FIGS. 29 and 36. Also in FIG. 42, allcombinations of TAP/STP and TAP domain arrangements 4201-4207 are shownbeing accessible between TDI/SI and TDO/SO during TAP controlled datascan operations, as previously described in regard to FIGS. 30 and 37.However, in FIG. 43 it is seen that only the TAP/STP domainsarrangements 4301, 4303, and 4307 can be connected between TDI/SI andTDO/SO and accessed using STP control. Connecting the Core 1 TAP domaininto the STP controlled arrangements of 4302, 4304, 4305, and 4306 wouldnot work since the TAP interface of Core 1 would not be able to shift,update, and capture with the STP control applied on TMS/CS. For example,if the TAP interface of Core 1 were included in arrangements 4302, 4304,4305, and/or 4306, it would attempt to interpret the STP's shift,update, and capture control on TMS/CS to transition through the TAPcontroller state diagram of FIG. 2. This would clearly corrupt anddisable the STP controlled shift, update, and capture operations to theTAP/STP interface(s) within the 4302, 4304, 4305, and/or 4306arrangements. Thus the TLM architecture of FIG. 31 advantageously servesto selectively partition conventional legacy TAP interfaces from TAP/STPinterfaces during STP controlled access.

It should be understood that while FIGS. 9, 11, 15, 17, 18, 21, 23, 24,31, 39, and 40 and accompanying descriptions have depicted the presentinvention as it would be applied and used to select core TAP/STP domainswithin an IC, the present invention can also be similarly applied andused to select sub-circuit TAP/STP domains within individual cores aswell. For example, FIG. 9 could depict sub-circuits 1-N in a core, eachsub-circuit having a TAP/STP interface connected to a core level scanpath 910. FIG. 31 could depict sub-circuits in a core, each sub-circuithaving a TAP/STP interface connected to input and output circuitry 3101,3102 and TLM circuit 3103 in the core. FIG. 40 could depict sub-circuitsin a core, some sub-circuits having TAP/STP interfaces and some havingTAP interfaces and all connected to input and output circuitry 3101,3102 and TLM circuit 3103 in the core.

Furthermore, it should again be understood that while FIGS. 9, 11, 15,17, 18, 21, 23, 24, 31, 39, and 40 and accompanying descriptions havedepicted the present invention as it would be applied and used to selectcore TAP/STP domains within an IC, the present invention can also besimilarly applied and used to select IC TAP/STP domains on a multi-chipmodule, a board, or a higher level circuit block, such as a systembackplane. For example, FIG. 9 could depict ICs 1-N on a board, each IChaving a TAP/STP interface connected to a board level scan path 910.FIG. 31 could depict ICs on a board, each IC having a TAP/STP interfaceconnected to input and output circuitry 3101, 3102 and TLM circuit 3103on the board. FIG. 40 could depict ICs on a board, some ICs havingTAP/STP interfaces and some having TAP interfaces and all connected toinput and output circuitry 3101, 3102 and TLM circuit 3103 on the board.

Additionally, while the present invention has shown the use of a dualmode test access port wherein the first mode is TAP controlled and thesecond mode is STP controlled, the dual mode port concept is general andcan be applied to other type of first and second mode controls as well.For example, a dual mode test access port may be implemented wherein theTAP control is used for the first mode and a control different from theSTP control is used for the second mode. This alternate second modecontrol was implied earlier in regard to the alternate STP “back toback” capture control operation description of FIG. 8B.

1. A process of selecting between an internal scan test port and a testaccess port, comprising: A. initially enabling the test access port anddisabling the scan test port; B. shifting scan test port selection datainto an instruction register of the test access port; C. performing aninstruction register update to output the scan test port selection datato select the scan test port and disable the test access port; D.operating the scan test port including shifting test data into aninternal scan register, capturing test data in the internal scanregister, and shifting test data out of the internal scan register usingcontrol and data leads of the test access port; E. holding a captureselect signal of the scan test port low for plural clock signals tode-select the scan test port and enable the test access port.
 2. Theprocess of claim 1 in which the shifting test data includes shiftingtest data across a data input lead common to the scan test port and thetest access port and shifting test data across a data output lead commonto the scan test port and the test access port.
 3. The process of claim1 including carrying clock signals across a clock lead common to thescan test port and the test access port.
 4. The process of claim 1including carrying test mode select signals and capture select signalsacross a lead common to the scan test port and the test access port. 5.The process of claim 1 including operating a test access port controllerto effect the shifting scan test port selection data and the performing.